Steel slabs commonly are conditioned by moving scarfing units along the top, bottom, and side surfaces of a steel slab to eliminate surface defects such as cracks, seams, and slag intrusions. One conventional scarfing apparatus includes top, bottom, and opposite side scarfing units that are mounted across the width and end portions of a support, to concurrently scarf all sides of the slab as the slab is passed therebetween.
Both top, side, and bottom scarfing units all include a manifold and head assembly, which receives and distributes oxygen and fuel gas to upper and lower preheat blocks. The upper and lower preheat blocks are spaced from each other to define between the two blocks an oxygen scarfing slot through which a quantity of oxygen is blown onto the slab surface to enable scarfing. The lower preheat block includes a fuel gas channel having a discharge opening positioned adjacent to the oxygen slot for discharging a fuel gas adjacent to the oxygen flow.
As illustrated for example in U.S. Pat. No. 4,115,154, the upper preheat block typically is a one-piece unit that includes oxygen and fuel gas channels each having discharge orifices to define nozzles through which a combination of oxygen and fuel gas is discharged for preheating the slab before scarfing. Later, a postmix flow of oxygen and fuel gas provides for scarfing. To maintain a proper vertical stand-off distance of the nozzle exits from the steel slab, the top and bottom scarfing units include riding shoes positioned on respective lower preheat blocks. Because the integrally formed nozzles do not provide for a high speed gas flow outward from the scarfing units, the total diagonal stand-off distance, i.e., the vertical stand-off distance and horizontal stand-off distance (the lead distance from the scarfing unit to the slab) is small, and the scarfing units must be placed in close proximity to the slab during preheating. Thus, in a conventional scarfing unit as illustrated in the above referenced patent, the upper preheat block extends forward and hangs over the lower preheat block to direct the preheating stream of gas discharged from the upper preheat block onto the slab during preheating.
Because the upper preheat block extends forwardly beyond the lower preheat block during initial preheating of the slab, the molten steel formed on the slab edge may drip onto portions of the upper preheat block positioned below the slab. The molten steel may damage the upper preheat block requiring reconstruction or replacement of the preheat blocks. To avoid this problem, during initial preheating, the scarfing units are positioned adjacent to the slab and heat the slab one to two inches inward of the end to prevent steel and slag from dripping onto the forwardly extending preheat block. As a result of starting the scarfing process inward from the end of the steel slab, the one or two inches of unscarfed steel must be either scrapped or hand scarfed, leading to excessive production costs.
Additionally, through continued use, the discharge ends forming the upper preheat nozzles may wear. Because the preheat nozzles are integrally formed in the upper preheat block, any damage to the nozzle area mandates either replacement of the entire upper preheat block, or removal of the damaged area and the brazing of new material onto the upper preheat block.
It is an object of the present invention to provide a scarfing apparatus that allows a greater diagonal standoff distance from the metal workpiece during preheating and initial scarfing, and so that significant quantities of molten metal are not blown onto the scarfing apparatus.
It is a more particular object of the present invention to provide a block assembly for a scarfing apparatus which includes a number of nozzles for directing a high speed preheating gas stream toward the workpiece with the gas stream comprising separate streams of oxidizing gas and fuel gas, which are adapted to be ignited at a substantial distance from the scarfing apparatus, and so that particles of molten metal are not blown onto the apparatus in significant quantities.
It is a further object of the present invention to provide a block assembly for a scarfing apparatus of the described type, and which includes a gas distribution network internally within the block assembly for efficiently and effectively distributing two separate gases, namely oxygen and fuel gas, to each of the nozzles of the apparatus.